Anti-microbial peptides (AMPs) are an evolutionarily conserved class of proteins that form an essential line of defense against microbial invasion. These peptides are produced by many disparate organisms and have been found to exhibit a wide spectrum of activity against bacteria, fungi (including yeasts), protozoa (including parasites), and viruses.
AMPs can be divided into four main structural groups: stabilized β-sheet peptides with two to four disulfide bridges; loop peptides with a single disulfide bridge; α-helical peptides; and extended structures rich in arginine, glycine, proline, tryptophan, and histidine. Typically 12 to 50 amino acids in length, these peptides are usually cationic with an amphipathic character. These biophysical properties allow them to interact with bacterial membranes resulting in either disruption of membrane integrity or translocation into bacterial cells and disruption of intracellular processes.
The alpha-helical structural motif of AMPs can be important to the ability of AMPs to interact with bacterial membranes. Upon binding to the membrane, AMPs can either translocate or insert themselves and permeabilize the membrane through a barrel-stove mechanism, a carpet-like mechanism or a toroidal pore mechanism. This process of permeabilization and disruption of membrane integrity can account for the antimicrobial properties of alpha-helical AMPs.